I've been playing a little with LibraryFind, a free and open source Federated Search. The project is very active - and seems to have gone a very long way to filling the gaping hole in this area. Z39.50 support seems well established: It took just minutes after install to get the application running with several library catalogues - including CISTI's. However, SRU support is currently restricted to MarcXML, with Dublin Core on the way (I need MODS!). It also does Open Search and OAI-PMH - but I've not played much with those aspects.
Anyone interested in using or demonstrating the SRU functionality may be interested in the following configuration information - as I had a difficult time to get a working example of SRU running... mainly due to the aformentioned lack of support for MODS:
Alt name: Willamette Dspace SRU
Conn type: sru
Record schema: marcxml
Mat type: Article
Vendor url: http://libmedia.willamette.edu/
Is parent: 0